It has long been a practice to use an elongated tubular member connected with fittings at each end to show the level of liquid in a containment vessel when attached thereto. This type of liquid level indication is commonly used because it is inexpensive and is fail proof since it does not depend on any mechanical or electrical mechanism to indicate liquid level.
One problem associated with the use of sight tubes for indicating liquid level is the danger of breakage. Any small diameter elongated tube of transparent material, whether glass or plastic, is susceptible of being broken by tools, broom handles, wind-blown objects and so forth. If a sight tube is broken, spillage of liquid contents from the containment vessel can be a problem. The problem can be particularly serious if the contents are hazardous, such as combustible liquids.
Others have provided protective sight gauges. A particularly relevant reference is U.S. Pat. No. 4,693,117 issued on Sep. 15, 1987 entitled “Replacement Element For A Liquid Level Gauge Sight Tube”. This patent shows a sight tube arrangement having upper and lower tubular portions that can be expeditiously received in compression type fittings secured to a vessel. This patent teaches a tubular gauge having a metallic shield member surrounding three sides of the sight tube and a transparent window closing the front of the shield. This type of liquid level sight gauge has proven very effective in providing increased safety since the sight tube is protected from inadvertent breakage. However, the system of U.S. Pat. No. 4,693,117 has the disadvantage in that tubular gauge has to be connected to additional components on each end to enable it to be connected to the containment vessel.
For further background material to sight gauges, see the following previously issued U.S. Pat. Nos. 635,565; 657,329; 743,178; 837,467; 845,258; 998,104; 1,006,105; 1,110,974; 1,132,372; 1,157,708; 1,159,764; 1,227,196; 1,239,304; 2,533,490; 2,792,710 and 5,442,959.
A large percentage of applications for liquid level gauges in process industries are low to medium pressure applications of less than 500 psig. These sight gauges use a clear sight tube for easy viewing of the liquid level. The materials of the clear sight tube are either glass or a transparent type of plastic (such as polycarbonate). Mechanical gauges are commonly installed onto tanks (a.k.a. “containment vessels”) using several different methods:    1. In-line level gauge installed between a tubular valve at either end. The gauge and tubular valves are separate entities. The gauge is fabricated to fit between the customer supplied centerline distance between the tubular valves.    2. Gauge with 90° connections for threading directly into tank. No valves of any sort (for control of inventory) are included in this configuration.    3. The third method combines a level gauge and tubular valves into one construction. The valves on either end have a ball check shutoff to isolate gauge and containment vessel if an unequalized pressure condition exists (such as when sight tube breakage occurs). The offset valve design allows easy access to the sight tube for cleaning, removal or routine maintenance.
The present invention advances the art and resolves longstanding problems associated with all of the above constructions. The following further elaborates upon problems common to gauges of the contemporary art.    1. Gauge is built with incorrect centerlines. In the design stage, the systems designer will specify a centerline dimension for the level gauge. In actual fabrication of the containment vessel, the vessel fabricator, for several different reasons, may not be able to hold the centerline dimension desired. Expensive rework and labor will add cost and aggravation to completing the containment vessel/level gauge assembly.    2. Additional fittings are required. In many cases, several additional fittings, such as unions and valves, must be mated together to complete the assembly.    3. Leak Points. There are several leak points in the installations listed above. There is the potential for a leak between the gauge and whatever control valve is installed. Unions might be required to connect the gauge to the tank. All of these additional connections add cost and labor to the gauge and vessel assembly process.    4. Safety. In many configurations, the sight tube component of the level gauge is exposed to environmental elements. If sight tube breakage occurs, there is the potential for operator injury and exposure to chemical and/or a chemical spill.
The gauge of the instant invention advances the art disclosed and claimed in the background material by disclosing an armored liquid level gauge with integral valves, ball check shutoffs and misalignment union vessel connections. The invention's innovative misalignment union structure provides for a gauge assembly that accommodates up to a ¼″ of misalignment between the level gauge and containment vessel centerline connections.
Although misalignment unions have been available, such unions have never been incorporated into an armored level gauge assembly with integral valves and ball check shutoffs. Consequently, unions and other fittings normally required of a piping configuration into the containment vessel are now an integral part of the level gauge via the teachings of the instant invention. This lowers the total cost of the level gauge and containment vessel assembly and minimizes the number of potential leak points associated with the additional fittings required with other types of level gauges.